Focus is a muscle. Every time you resist the urge to check something mid-task, you strengthen it. Every time you give in, you weaken it. The young people who can sit with a hard problem for two hours without reaching for a distraction are developing something most people around them are losing. The discomfort you feel when you start a focused session — the restlessness, the urge to check, the sense that you should be doing something else — is not a sign that something is wrong. It is a sign that the muscle is being worked. The more you practise staying, the longer you can stay, and the more you produce in the time you have.